As far as opening releases go for a new game, this could well be up there with the very best.
Not only is it a HUGE update, the writing is great (as others have said) and there's a clear progression with the standard compared to their first three games (DMD, Melody and Sunshine Love). Love the MC's sense of humour which makes him quite likeable ( a rarity with MC's).
There's a big improvement in the quality of the animations.
There were glimpses in SL that they were getting better with them and you can see the full extent of that in this new game.
The approach to how they've crafted each scene is more focused: you can tell that more time and care has been taken in the detail shown for each scene.
This dev team gives you more than enough details about all the main characters in the game while also leaving some mystery and intrigue with others. Basing the story around a group of thieves definitely helps in this regard.
There's a decent mix in terms of the age of the love interests - two of which are only a couple of years in difference, either side of the MC's age (21).
It could do with another younger character but it's still only the first update, so plenty of room and time to add more.
Some of the MrDot formula still remains, but it works for Thief of Hearts and most mistakes of previous games haven't shown up in my playthrough so far.
Look out for the odd references to well-known films and TV shows - something I've noticed with their previous works.
There are a few inconsistencies with rendering details/errors but that would be purely nitpicking.
As for extras in the game, there's a stack of bonus images and quite a number of hidden and bonus scenes which gives players a reason to go through the game again. It's not for everyone, but it's a nice inclusion nonetheless.
Anyway, try it for yourself and come up with your own opinion.
Forget about their previous work or what the negative Nancy's are saying -
if they had anything resembling actual talent they'd make their own game.
They wouldn't know what hard work and putting in plenty of effort looks like, which is clearly evident in the creation of this first update.
Thief of Hearts is something fresh from this team, and there's a clear progression in quality here.
Looking forward to the next update already!